The present invention relates to a device for the improvement of the running conditions in a hydraulic installation or in a so-called hydraulic system.
A hydraulic system is normally designed with a suction pipe connecting an oil tank to a pump or pumps of a system which directly or indirectly supply the executive units of the system with hydraulic power in the form of hydraulic motors and cylinders. Hydraulic fluid is returned from motors and cylinders to the tank through a return pipe and possibly collected leakage is brought back by means of a drain pipe. The oil tank communicates with the outside air through an airfilter. Because of variations in the enclosed oil volume of the hydraulic system and because of the temperature-depending volume variations, the oil level in the tank will vary and the air in the tank will breathe through the mentioned filter.
Despite the filter, small dirt particles will always pass to the oil from the ambient air and reversedly, at the same time, a limited continous evaporation of oil to the outside air is going on.
Furthermore, the outside air contains water vapour which will condense as water on the cooler inside walls of the tank when the temperature drops below the current saturation temperature of the air. This causes the hydraulic fluid, over a period of time, to be super-saturated with water, resulting in the presence of water in free form in the tank.
Via the contact with the atmosphere, the hydraulic fluid will furthermore be saturated with air. Hydraulic fluid in the form of mineral oil dissolves, e.g., 9 percentage of volume air at room temperature and atmospheric pressure. With dropping pressure, the value of saturation decreases, so that one normally has to take into consideration a certain amount of free air in, e.g., suction pipes in which, related to the atmospheric pressure, a negative pressure easily appears. The hydraulic fluid and certain components, which are parts of the system, are also continuously exposed to oxidation because of the oxygen in the dissolved air.
Air as well as water and dirt particles, i.e., the impurities, are thus not wanted in a hydraulic system, and the availability of the whole system is dependent upon a low level of the mentioned impurities. Another disadvantage which is the result of what has been alleged above is the following:
As mentioned before, the tank is connected to a pump. The suction pipe is dimensioned considering the pressure drop in the pipe between the tank /pump-inlet which leads to a design of short and coarse suction pipes. Despite this dimensioning, problems of cavitation appear at the pump inlet, because of too low a pressure, which particularly occurs if the hydraulic fluid is heavy. The foremost reason for these conditions is normally that the hydraulic fluid in the tank is more or less saturated with air which to a certain extent is dissolved in the suction pipe when the static pressure in the suction pipe drops below the atmospheric pressure.
The known systems comprise filters, sometimes placed in separate filter circuits, and sometimes just as return filters, i.e., fitted in the return pipe. Separate coolers control the temperature of the hydraulic fluid.
As understood by the introductory description, it is not possible in normally designed hydraulic systems to efficiently prevent new particles, water and air from getting into contact with the hydraulic fluid. Furthermore, there is a great risk of cavitation at the suction connections of the pumps, because only atmospheric pressure is available for feeding the pump with hydraulic fluid. The mentioned drawbacks result in problems with, 1.a., component wear, rust damage, rapid fast oil oxidation and cavitation damage.